1. Field of the Invention
The invention concerns a process for glazing a material web, in particular a paper web, in which the material web is guided through at least one nip, which is formed by a roller having an elastic covering made of a plastic reinforced with fibers or appropriate fillers and an opposing roller. The invention further concerns a roller for a glazing calender with a uniform structure on its surface.
The invention is explained in the following with reference to a paper web as an example of a material web. It is, however, also applicable with other material webs for which the conditions are similar.
2. Discussion of Background Information
In one of the final production steps, a paper web is glazed, i.e., guided through at least one, but usually a plurality of nips or roll gaps of a calender, where it is subjected to pressure and high temperature. The paper web is more than merely compacted by this. It is also desirable to influence other properties of the paper web, for example, glaze and smoothness. Another property which can be influenced during glazing is transparency. In printing papers, high opacity, i.e., low transparency, is often desired. In contrast, in so-called technical papers, such as silicon paper, glassine, and drawing paper, high transparency is often desired.
High transparency is obtained with prior art super-calenders when glazing is performed under high temperature, high pressure, and high humidity. Here, a black glazing undesirable in other papers, is deliberately produced. It is assumed that in this glazing the paper fibers are crushed to a point at which light permeability is, in contrast, possible.
Tests have demonstrated that transparency may be deliberately influenced only with relatively great difficulty using plastic rollers, i.e., rollers with an elastic covering made of a fiber-reinforced plastic. In particular, it has been relatively difficult to date to produce high transparency using plastic rollers.